Try checking the value of errno....
Older UNIX methods would return -1 on failure and set errno to the actual
specific error.
-----Original Message-----
From: Patrick Frants [mailto:patrick@quintiq.com]
Sent: February 26, 2002 12:43 PM
To: pthreads-win32@sourceware.cygnus.com
Subject: sem_trywait never returns EAGAIN
Hi,
>From the Linux man pages I concluded that calling sem_trywait on a semaphore
with a zero count should result in an EAGAIN return value. I get a -1 all
time
time. Intiializing the count with 1 and calling sem_trywait two times
results in 0 and -1 return codes. Initializing with 0, calling sem_trywait
results in a -1 return
code. Initializing with 0, calling sem_post, and sem_trywait twice results
in 0 and -1 return codes for the sem_trywait calls.
Are my expectations wrong or is the behaviour of the library wrong?
Here is my sample code:
#include <pthread.h>
#include <semaphore.h>
#include <cassert>
#include <cstdio>
#pragma comment(lib, "pthreadvce")
int main(int argc, char** argv)
{
sem_t s;
assert(sem_init(&s, 0, 0) == 0);
int result = sem_trywait(&s);
if ( result == -1 )
{
perror("sem_wait"); // No error
}
else
{
printf("ok\n");
}
result = sem_post(&s);
result = sem_trywait(&s);
if ( result == -1 )
{
perror("sem_wait");
}
else
{
printf("ok\n");
}
return 0;
}
--
Patrick Frants
Senior Software Engineer
Quintiq
patrick@quintiq.com
www.quintiq.com
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